Sunan an-Nasa'i, Hadith 1328 ⓘ
It was narrated from 'Urwah (that) Aishah said: "The Messenger of Allah used to pray eleven rak'ahs, making it odd (witr) by one between the time when he finished 'Isha and dawn, and he would prostrate for as long as it takes one of you to recite fifty verses before raising his head."
أَخْبَرَنَا سُلَيْمَانُ بْنُ دَاوُدَ بْنِ حَمَّادِ بْنِ سَعْدٍ، عَنِ ابْنِ وَهْبٍ، قَالَ أَخْبَرَنِي ابْنُ أَبِي ذِئْبٍ، وَعَمْرُو بْنُ الْحَارِثِ، وَيُونُسُ بْنُ يَزِيدَ، أَنَّ ابْنَ شِهَابٍ، أَخْبَرَهُمْ عَنْ عُرْوَةَ، قَالَ قَالَتْ عَائِشَةُ كَانَ رَسُولُ اللَّهِ صلى الله عليه وسلم يُصَلِّي فِيمَا بَيْنَ أَنْ يَفْرُغَ مِنْ صَلاَةِ الْعِشَاءِ إِلَى الْفَجْرِ إِحْدَى عَشْرَةَ رَكْعَةً وَيُوتِرُ بِوَاحِدَةٍ وَيَسْجُدُ سَجْدَةً قَدْرَ مَا يَقْرَأُ أَحَدُكُمْ خَمْسِينَ آيَةً قَبْلَ أَنْ يَرْفَعَ رَأْسَهُ . وَبَعْضُهُمْ يَزِيدُ عَلَى بَعْضٍ فِي الْحَدِيثِ . مُخْتَصَرٌ .
also referenced under: Book 13, Hadith 150 (In-Book) & Volume 2, Book 13, Hadith 1329 (DarusSalam)